FIG. 8 is a view illustrating a battery charging device used in a two-wheeled vehicle and the like.
A permanent magnet type of three-phase alternating current generator (referred to below simply as an ‘alternating current generator’) 1 is driven to rotate from an engine side (not shown). Three-phase alternating current that is output from the alternating current generator 1 is rectified (undergoes alternating current/direct current conversion) by a battery charging device 3A so as to become direct current output, and charging current is supplied to a battery 2 by the direct current output.
In this case, in order for the battery charging to be performed efficiently, advance angle/delay angle control is conducted which controls the power generation amount of the alternating current generator 1. This advance angle/delay angle control is achieved by forming a rectifier circuit inside the battery charging device 3A from switching elements that have a bridge configuration, and then advancing or delaying the electricity supply timings of these switching elements relative to the phase of the alternating current output voltage of the alternating current generator 1.
In this advance angle/delay angle control, the power generation amount of the alternating current generator 1 is controlled using an advance angle/delay angle amount as a control parameter. When the voltage of the battery 2 is lower than a reference voltage and requires battery charging, delay angle control is performed on the battery charging device 3A and the battery is charged. When the voltage of the battery 2 is higher than the reference voltage and does not require battery charging, advance angle control is performed on the battery charging device 3A and energy is discharged from the battery to the alternating current generator.
In this case, as is shown in FIG. 9, in a delay angle control state, it is possible to gradually increase the power generation amount (the battery charging amount) by increasing the delay angle amount from 0. However, although it is possible to raise the power generation amount up to a particular fixed delay angle amount, if this fixed delay angle amount is exceeded, then, conversely, there ends up being a reduction in the power generation amount. Accordingly, it is necessary to set the value of the limit of the delay angle amount (referred to below on occasion as the ‘delay angle limit value’) where the amount of power generated by the alternating current generator 1 is at the maximum, to a suitable value.
When setting this delay angle limit value, conventionally, combined tests (experiments) are performed in accordance with the alternating current generator that are actually being used, the type of battery, and the size of the engine (the displacement), and the optimum delay angle limit value is then determined.
In this manner, a large number of tests are carried out in order to determine the optimum delay angle limit value, requiring considerable labor including making tables showing corresponding relationships between the delay angle limit values, the alternating current generators, the batteries, and the displacements determined from the results.
This conventional type of output control device for a synchronous motor is described in Patent document 1. The conventional technology has the objects of eliminating unnecessary power generation by controlling fluctuations in the power generation amount, and performing battery charging properly while maintaining a superior acceleration performance. Because of this, the control voltage value that is used to control the generated voltage is set as a function of the engine speed for both accelerating and for normal running. Namely, the control voltage value is decided in accordance with a determination of acceleration which is made based on the engine speed and the throttle opening angle, and an advance angle/delay angle amount setting section decides the energization timing to each phase of the stator coil such that the battery voltage is converged to the control voltage value.
However, the above described conventional technology aims to perform battery charging properly while maintaining a superior acceleration performance and is not intended to solve the problem of excessive labor being required in order to set the optimum delay angle limit value in accordance with the combination of the alternating current generator, the type of battery, and the displacement.    [Patent document 1] Japanese Unexamined Patent Application, First Publication No. 2004-194427